Toothbrush handle having an inner cavity

ABSTRACT

A personal care article, such as a toothbrush handle having an inner cavity.

FIELD OF THE INVENTION

The present invention relates to toothbrush handles having an innercavity.

BACKGROUND OF THE INVENTION

Toothbrushes are typically manufactured using an injection moldingprocess. Such an injection molding process is characterized by providinga mold in the shape of the toothbrush and injecting molten plasticthrough a hot channel nozzle into the mold. The toothbrush is thencooled and ejected from the mold. For example, U.S. Pat. No. 5,845,358shows such a toothbrush made by injection molding. One of thelimitations of the conventional injection molding processes is thatlarge diameter handles, and especially large handles with a substantialvariation in cross sectional area where cross sectional area bothincreases and decreases along the length or major axis of the brush,cannot be produced in an efficient manner, due to the cost of increasedmaterial and lengthened cooling times, resulting from the increased massof material used. A second significant limitation of conventionalinjection molding is that it requires multiple steps, multiple injectionnozzles and multiple cavities or cavity sets to make amultiple-component brush.

Toothbrushes with increased handle diameters provide substantialadvantages, for instance they can provide increased gripping area forchildren, increasing the ability of children to handle and usetoothbrushes; also people with disabilities such as arthritis sometimeshave difficulty in handling toothbrushes due to difficulty in flexingthe joints in their hands. Such difficulties are considerably relievedby means of toothbrushes having increased handle diameters.Additionally, the larger cross section handles on the toothbrushes arebetter for the user from an ergonomic point of view.

Toothbrushes with high-friction and/or low-durometer regions of a secondmaterial on the outer surface also provide substantial advantages ingripping. Low-durometer materials, such as those materials whosehardness is measured at less than approximately 90 on the Shore A scale,provide advantages in grip by deforming under the range of comfortablegripping forces. The deformation assists in holding the brush uniformlyin position in the hand, and also provides a pleasing tactile feedback.Addition of high-friction grip surfaces directly reduces the squeezingforce necessary to maintain a stable orientation of the brush bristlesduring use. Due to their low strength, however, toothbrushes madeentirely from high-friction, low-durometer material are unlikely toexhibit the bend strength necessary to provide adequate force to brushin a conventional grip style. Thermoplastic Elastomers (TPEs) in thehardness range of Shore A 20-90 are a common second, third or subsequentmaterial used to improve grip on toothbrushes and other personal carearticles.

Variations in cross sectional area, including both larger and smallercross sectional areas, along the length or major axis of the brushassist the user in the grip and handling of the brush during use, whenit must be rapidly moved while it may also be wet or slippery.Additionally, materials that maintain a higher coefficient of frictionwhen wet, including TPEs in the abovementioned hardness range can assistin wet-grip situations.

In an attempt to overcome the difficulties associated with the use ofinjection molding to produce toothbrush handles having increaseddiameters, it has been suggested to produce toothbrush handles having ahollow body. For example, EP 0 668 140 and EP 0 721 832 disclose the useof air assist or gas assist technology to make toothbrushes havinghollow, large cross-sectional handles. In the disclosed process, moltenplastic is injected near the base of the toothbrush handle, whereinsubsequently a hot needle is inserted into the molten plastic to blowgas into the molten plastic which is then expanded towards the walls ofthe injection mold. In a similar manner, U.S. Pat. No. 6,818,174 B2suggests injecting a predetermined amount of molten plastic into thecavity to only partially fill the mold cavity and subsequently inject agas through a gas injection port formed in the injection mold to forcethe molten plastic into contact with the walls of the mold cavity. Suchinjection molding processes using additional air injection havesubstantial difficulty forming hollow handle bodies with substantiallyuniform wall thickness, and as such, the potential for optimization of ahandle for maximum ergonomic function in minimum material weight andmanufacturing efficiency is limited. A further drawback to suchinjection molding processes is the creation of a vent hole for the gas.EP 0 668 140 provides a possible solution to this problem via use of amoving injection pin to create a sealed part, however the integrity ofthis seal under the injection molding pressures created in the secondshot is highly sensitive to processing conditions and may not result ina reliably-sealed part. The vent hole is formed at the interface ofmolten plastic and high-pressure gas (and not by mold steel) and thuscannot be made predictably or with high precision. A still furtherdrawback of hollow-handled toothbrushes made using gas-assist injectionmolding relates to the application or installation of a second, third orsubsequent material to the toothbrush by injection molding, orovermolding, where the overmolded material may, in the process ofsealing the necessary gas vent, intrude substantially into the hollowvoid created in the first gas injection step, as there is nothing tostop it besides friction and the near-atmospheric pressure inside thevoid. EP 0 721 832 illustrates this effect in detail. While this maystill result in a cosmetically-acceptable part, it prevents use ofshot-size-limiting devices such as valve gates and can add substantiallyto the cost of the part. Gas-assist injection molding does notsubstantially reduce injection pressure or melt energy required to forma plastic article, and most gas-assist injection molding prior artclaims a void volume that is only 10-50% of the total part volume, andmore often 10-25% of the total part volume

A conventional method to create toothbrush handles having increasedcross sections, such as electromechanical toothbrush handles, is tomanufacture discrete parts of the handle separately using injectionmolding, then to assemble these parts in either a separate non-injectionmolding step, or in a subsequent injection molding step, or most oftensome combination of the two, whereby the discrete parts from the firststep or steps are inserted into an injection mold first and one or moreadditional materials are injected around them, creating a hollow bodyfrom multiple parts. This manufacturing method still has the drawbacksof: requiring the complete melting of plastic, high pressures andassociated equipment involved with injection molding, and in additionmay have added labor expense associated with both in-mold andout-of-mold assembly of discretely-molded parts for the handle. The useof injection molding to create multiple discrete parts also has thedisadvantage that each part must not contain any substantial undercutfrom which the mold core forming a concave surface of theinjection-molded part could not be extracted from the part after moldingFurther, mold cores must typically contain some mechanism to cool orremove heat, typically embodied as internal channel through whichchilled water is forced, and would thus be difficult or impossible tocreate to make internal geometry for most manual toothbrushes which mayhave diameters less than 10 mm and lengths beyond 150 mm. The lack ofundercuts in discrete parts combined with the length and diameter ofcores required to make non-undercut handle parts combined with thedesire for multiple areas of variation in cross sectional area on atoothbrush handle would thus require any discretely-assembled handles tohave multiple mating surfaces, which would preferably require seals tomaintain barriers to moisture and debris, even under time and repeateduse.

Installation of soft-touch or second materials to hollow molded articlescan be made by other means such as welding, gluing or use of flexibilityof the soft-touch material to itself grip an undercut pre-molded intothe main article. These methods all have disadvantages however inlong-term adhesion, especially to thermoplastics with less-activesurfaces made from materials such as polypropylenes. Durable articlesmade from multiple components which must be used in unpredictablecircumstances and environments such as consumers' bathrooms mustnecessarily be constructed more robustly than for example, disposablearticles or packages.

Electromechanical toothbrushes in particular are susceptible to problemsof assembly, as they are necessarily hollow in order to includebatteries, motors and associated electrical linkages and drivecomponents which must be all placed inside with some degree ofprecision. To avoid the problems and expense of welding plastic partstogether and multiple assembly steps of a sealed outer shell, it hasbeen proposed to blow mold the handle for electromechanicaltoothbrushes. In the assembly of a blow molded electromechanicaltoothbrush it is necessary to leave the blow molded portion of thehandle open in at least one end to accommodate the motor, batteries, anddrive system components. In this process, the minimum diameter of atleast one opening to the blow molded handle must exceed the smallestlinear dimension of every component that will be inserted. Such a largeopening would be a drawback in a non-electromechanical handle, which hasno need to accommodate internal component entry, and would necessitatean overly-large second part or cap to prevent intrusion and collectionof water, paste, saliva and other detritus of conventional use. Such anoverly-large opening, if positioned near the head, would interferesubstantially with ergonomic use of the brush. Additional constraints tothe geometry on the inside surface of the cavity, for example to locatemotors, housings, batteries, etc. which must be positioned insideaccurately as to be rigidly fixed will also be detrimental to theoverall blow molding process, as the majority of the inner cavitysurface of a blow molded part cannot be defined directly by steel orother mold material in the mold surfaces, and is instead definedindirectly by steel or other mold material on the outer surface of thehandle combined with the wall thickness of the parison, blowing pressureand stretch ratio of the final part to the original parison or preformthickness. Such constraints of these process variables will necessarilylimit manufacturing efficiencies.

To accommodate activation of electrical components via a standard buttonor mechanical switch, at least some portion of a blow moldedelectromechanical toothbrush handle should be made thin enough to flexsubstantially under pressure of a finger or hand squeeze. Such athin-walled structure or film-walled structure necessarily requires somestrengthening mechanism to ensure durability and rigidity under use. Aninternal frame or cap, as described in WO 2004/077996 can be used toprovide this necessary strengthening mechanism in an electromechanicaltoothbrush, but would be a drawback to a manual brush, which does notrequire additional components to function adequately, in extra expense,complexity and additional load-bearing parts. Further, due to the linearnature of the motor, power source, and drive shaft of electromechanicaltoothbrushes there are no or minimal variations to the cross-sectionalarea of the inner cavity; such that the inner cavity walls providemechanical support to the internal components to reduce or eliminateunwanted movement or shifting.

An electromechanical toothbrush handle, made by blow molding orinjection molding, is typically manufactured with an opening at eitherend: At a distal end there is typically an opening to accommodate themechanical translation of power through a drive mechanism to thetoothbrush head, and at a proximal end there is typically an opening toaccommodate insertion of components during manufacturing and possiblyalso insertion or removal of the battery by the user. Such a secondopening would be unnecessary for a manual toothbrush and would createdrawbacks in the need for additional seals and mechanical fasteners. Insome blow molding processes, the formation of openings at the distal andproximal ends of the molded part are intrinsic to the process and wouldbenefit the formation of a double-open-end handle, but would not benecessary for a manual toothbrush handle.

There are several advantages to making toothbrush handles lighter inweight overall, regardless of cross section or changes to the size.Lighter handles could provide a more tactile feedback of forcestransmitted from the teeth through the bristles to the head to thehandle to the hand during brushing. Lighter toothbrush handles wouldalso ship in bulk with greater efficiency from manufacturing centers toretail centers where they are purchased by users. To reduce weight whilemaintaining stiffness, some toothbrush handles are made from bamboo orbalsa wood, however these materials have disadvantages in that they arenot easily formable into complex three-dimensional shapes which can becomfortably gripped. Further, these materials are anisotropic, meaningthey have elastic moduli and yield strengths or ultimate strengths whichvary with the direction of applied load. Carbon-fiber composites andglass-filled injection-molded plastics are other common examples ofanisotropic materials which could be used to make lighter and strongertoothbrushes. Articles made from these materials must therefore beformed with their strongest axis or ‘grain’ aligned substantially withthe major axis of the article in order to resist fracture during thebending forces common to use. Both carbon fiber and glass-filledthermoplastic composites also tend to fail in a brittle manner, withlittle ductility. This type of failure is undesirable in a device thatis placed in the mouth. Further, these materials do not containintrinsically all of the properties necessary to create light weight,strength in bending and soft-touch, high-friction grip. This creates anextra necessary step in the preparation of the material prior to formingor machining. This alignment of the grain also can present a specificdisadvantage to woods in general in that the presentation of splintersof material is most likely to occur in the direction aligned to typicalforces applied by the hand during brushing.

To make toothbrush handles lighter without relying on anisotropicmaterials such as woods, the articles could be made lighter through theuse of non-homogeneous but isotropic materials, such as foamed plastics.Foamed plastics present an advantage in that they can offer a higherstrength-to-weight ratio than solid plastics without regard to materialorientation. The overall weight savings possible with foamed plasticsmay be limited however, as the bubbles inside the plastic which createthe weight savings also create stress concentrations which will severelyreduce strength in tension and will also severely reduce ductility priorto failure. While foamed plastics can provide substantial strength incompression (and are used for exactly this purpose in applications suchas packing materials where material weight combined with resistance tocompressive crushing is a critical issue) the weakness in tensionseverely affects bending strength and prevents uniformly-foamed plasticsfrom serving as load-bearing elements in articles which must maintainstrength, stiffness and ductility in bending during normal use.

It is familiar to those in the art to use extrusion blow molding tocreate single-component or single-material lightweight hand-heldarticles, such as children's toys, such as hollow, plastic bats, golfclubs or any large, plastic article which benefits from being lighter inweight. While these articles can be both stiff and strong in bending,they also generally contain drawbacks which would limit their generaluse in semi-durable, Class-I medical devices, such as toothbrushes.First, such articles typically contain significant flash along partinglines, or in any locations where the parison is larger in crosssectional area than is the cavity to which it is blown. In theselocations the parison folds within the cavity or is pinched off at thecavity party ling, and substantial flash is created. Second, mostarticles contain some significant vestige of blowing in the form of ahole, which may be accurately or inaccurately formed. Such a vestigewould be regarded as a significant defect in a Class-I medical devicewhich must prohibit breach or entry of contaminants to a hollow interiorwhich does not drain effectively. Third, the relative size of thesearticles is large in comparison to the size of these defects, and theoverall function of the articles is not severely affected by thesedefects. In many cases, the size of the article itself renders themanufacturing process easier, with respect to the minimization ofdefects. It is not challenging to extrusion blow mold articles, packagesor bottles in the size range common to manual toothbrush handles —if theplastic wall thickness can be minimized in proportion to the overallcross section. Such articles exist in the form of small, typicallysqueezable, tubes or bottles which in fact benefit from having a verythin, deformable wall which enables dispensing of internal contents, butalso makes them unusable or significantly inferior as toothbrushes.

Extrusion- and injection-blow-molded handles for single-componentsemi-durable consumer goods such as feather dusters and tape dispensersare also known but again these articles would not meet criteria forsemi-durable Class I medical devices, specifically with regard to thesealing of the necessary blowing orifice against intrusion of water orother contamination, and in the case of extrusion blow molding, in theappearance of flash on the articles in areas that would directly contactor go into the mouth. These articles can also be brittle, and when toomuch force is applied, can break or snap suddenly and without ductility,producing sharp edges, making them unusable for use in the oral cavity.

Multi-component blow molded packages, such as water bottles, are knownto those familiar in the art. In these embodiments, smooth blow moldedbottles are provided with tactile, high-friction surfaces via the use ofan in-mold labeling technique, whereby previously injection-molded,textured labels are placed into mold cavities prior to introduction andblowing of the semi-molten parison of extruded plastic. While thesearticles do provide the advantage of a large gripping surface which isimproved by addition of a high-friction textured surface, they are bynature highly-deformable or squeezable packages designed for liquidstorage and dispensing, and would serve poorly as toothbrushes.

It has also been proposed to manufacture manual toothbrushes by blowmolding, and in fact it should not prove challenging to extrusion blowmold, injection blow mold, or even injection-stretch blow mold such anarticle in the general shape and size of a toothbrush or toothbrushhandle, however no existing disclosure in the prior art addresses theissues of: Strength in bending, stiffness in bending, overall rigidity,mitigation of flash or other sharp defects, variations incross-sectional area and undercuts, and obstruction or sealing of theblow hole vestige. Any one of these defects in a blow molded toothbrushor toothbrush handle would severely affect the utility of the article,and as such, improvements are needed to enable a hollow article withmaterial savings maximized by uniform wall thickness which is suitablystrong and stiff in bending without breaking in use and does not leak orpresent uncomfortable defects to the user.

In view of these drawbacks of the prior art, it is an objective of thepresent invention to provide an improved toothbrush or toothbrush handlehaving an inner cavity, which avoids the drawbacks of the prior art.

SUMMARY OF THE INVENTION

A toothbrush handle is provided that comprises a terminal end, connectorend, outer surface, inner cavity, and longitudinal axis; the innercavity having a surface defining a cross-sectional area; wherein theinner cavity has at least one of a greater cross-sectional area,bordered by two lesser cross-sectional areas along the longitudinal axisof the toothbrush or a lesser cross sectional area bordered by twogreater cross-sectional areas along the longitudinal axis of thetoothbrush; the outer surface defines an outer surface cross-sectionalarea; a wall formed from the outer cavity surface and inner cavitysurface; and the toothbrush handle comprises a single unitary component,wherein the difference between the outer surface cross-sectional areaand the inner cavity surface cross-sectional area varies less than 25%over at least 50% of the toothbrush handle length along the longitudinalaxis.

A toothbrush handle is provided that comprises a terminal end, connectorend, outer surface, inner cavity, and longitudinal axis; the innercavity having a surface defining a cross-sectional area; wherein theinner cavity has at least one of a greater cross-sectional area,bordered by two lesser cross-sectional areas along the longitudinal axisof the toothbrush or a lesser cross sectional area bordered by twogreater cross-sectional areas along the longitudinal axis of thetoothbrush; the outer surface defines an outer surface cross-sectionalarea; a wall formed from the outer cavity surface and inner cavitysurface; the toothbrush handle comprises a single unitary component; andwherein the toothbrush handle comprises two or more material layers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a toothbrush handle according to anembodiment of the present invention.

FIG. 1A is a cross-sectional view of FIG. 1 along section line 1Aaccording to an embodiment of the present invention.

FIG. 1B is a cross-sectional view of FIG. 1 along section line 1Baccording to an embodiment of the present invention.

FIG. 2 is a perspective view of a toothbrush handle according to anembodiment of the present invention.

FIG. 3 is a perspective view of a toothbrush handle according to anembodiment of the present invention.

FIG. 4 is a perspective view of a toothbrush handle according to anembodiment of the present invention.

FIG. 5 is a perspective view of a toothbrush handle according to anembodiment of the present invention.

FIG. 6 is a perspective view of a toothbrush handle according to anembodiment of the present invention.

FIG. 6A is a cross-sectional view of FIG. 6 along section line 6Aaccording to an embodiment of the present invention.

FIG. 7 is a perspective view of a toothbrush according to an embodimentof the present invention.

FIG. 7A is a cross-sectional view of FIG. 7 along section line 7Aaccording to an embodiment of the present invention.

FIG. 8 is a perspective view of a toothbrush handle according to anembodiment of the present invention.

FIG. 8A is a cross-sectional view of FIG. 8 along section line 8Aaccording to an embodiment of the present invention.

FIG. 9 is a perspective view of a toothbrush handle according to anembodiment of the present invention.

FIG. 9A is a cross-sectional view of FIG. 9 along section line 9Aaccording to an embodiment of the present invention.

FIG. 10 is a perspective view of a toothbrush handle according to anembodiment of the present invention.

FIG. 10A is a cross-sectional view of FIG. 10 along section line 10Aaccording to an embodiment of the present invention.

FIG. 11 is a perspective view of a toothbrush handle according to anembodiment of the present invention.

FIG. 11A is a cross-sectional view of FIG. 11 along section line 11Aaccording to an embodiment of the present invention.

FIG. 12 is diagrammatical representation of a method of analysis.

FIG. 13 is diagrammatical representation of a method of analysis.

FIG. 14 is a chart illustrating deflection in bending vs. specificgravity.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to personal care articles having an innercavity, such as a unitary single-component toothbrush handle that mayhave different colors, forms, and surface decorations on either or bothof the inner cavity or outer surface. The toothbrush handle may be madein a single molding step. The inner cavity varies in cross-sectionalarea along the length of the toothbrush, wherein the inner cavity isessentially open as compared to an open or closed cell foam material.The toothbrush handle is a unitary piece, but may include separatenon-structural elements, such as labels, grip structures, etc. . . . Incertain embodiments the inner cavity is sealed with no opening to theouter surface of the toothbrush handle. In certain embodiments theunitary toothbrush handle is comprised of distinct regions of differentmaterials, which are intrinsically or chemically bonded to one anotheras a part of the manufacturing process.

Personal care articles are items used to store, dispense, apply ordeliver benefits to a consumer's personal health, beauty, grooming, orother body or human biological system care, maintenance, enhancement orimprovement. Examples of personal care articles include, but are notlimited to toothbrushes, toothbrush handles, razors, razor handles, mophandles, vacuum handles, makeup or beauty care applicators, skin careapplicators, feminine hygiene applicators, hair care applicators, haircolorant applicators, or hair care articles.

FIG. 1 shows an embodiment of a personal care article, a toothbrushhandle 10, having a terminal end 12 and a connector end 14. Thetoothbrush handle 10 may be unitarily formed as a single piece andcomprise an inner cavity 30 and an outer surface 50, wherein the handleouter surface 50 varies in cross-sectional area (OS_(CA))_(,) which isthe total area of the cross-section as defined by the outer surface 50,along the handle 10 longitudinal axis L—as shown in FIG. 1A; in thisembodiment the handle 10 has a substantially hourglass shape. The innercavity 30 has an inner cavity surface 32, wherein the inner cavitysurface 32 varies in cross-sectional area (IC_(CA)) along the handlelongitudinal axis L. As FIG. 1 shows, in certain embodiments the innercavity 30 of the handle 10 has one or more greater cross-sectional areasIC_(CAG) bordered along the longitudinal axis L of the handle 10 bylesser cross-sectional areas IC_(CAG), IC_(CAL2) having a smaller areathan the area of the greater cross-sectional area IC_(CAG). A handle 10inner cavity 30 may also have a lesser cross-sectional area IC_(CAL)bordered along the longitudinal axis L of the handle 10 by greatercross-sectional areas IC_(CAG1), IC_(CAG1) having a larger area than thearea of the lesser cross-sectional area IC_(CAL). Further, as shown inFIGS. 1, 1A and 1B, in certain embodiments the square root of the innercavity surface 32 cross-sectional area varies proportionally to thevariations in the square root of the outer surface 50 cross-sectionalarea along the longitudinal axis L of the handle 10, with the exceptionof the areas near the terminal 12 and connector end 14 of the toothbrushhandle where the inner cavity 30 becomes sealed. In certain embodimentsthe square root of the inner cavity surface cross-sectional area variesproportionally less than 5% to the variations in the square root of theouter surface cross-sectional area along the longitudinal axis L of thehandle 10 with the exception of the areas near the terminal andconnector end of the toothbrush handle. In certain embodiments thethickness of the toothbrush handle wall, the distance between thetoothbrush handle outer surface and the inner cavity surface, varies ininverse proportion to the square root of the outer surfacecross-sectional area. In certain embodiments the difference between theouter surface cross-sectional area (OS_(CA)) and the inner cavitysurface cross-sectional area (IC_(CA)) varies less than about 25%, 20%15%, 10%, 5% over at least 50%, 70%, 80%, 90% of the toothbrush handlelength along the longitudinal axis. For example, in these embodimentsareas of a toothbrush handle having a greater outer surfacecross-sectional area will have a thinner wall (compared to areas havinga lesser outer surface cross-sectional area) as the material has beenstretched to a greater degree during the extrusion blow molding process.

In certain embodiments, as shown in FIG's 2 and 3, a handle 110 may be apart of a toothbrush 100 along with a separate neck 150 and head 160.The handle 110 comprises a longitudinal axis (L), a terminal end 112, aconnector end 114, an outer surface 116 and an inner cavity 118 asdescribed previously.

In addition the handle 110 can be formed to include a connector 120 toengage a complementary connector 152 in the neck 150 to form atoothbrush 100. The connectors 120, 152 can be formed to allowreleasable or permanent connection between the handle 110 and neck 150in any manner known to one of ordinary skill in the art. For example,the connectors 120, 152 may be provided with connection features, suchas a screwing thread so the two connectors 120, 152 can be screwed toeach other. Alternately or in addition, one of the connectors 120, 152may possess a connection feature, such as a bulge, rib, or hookcorresponding to a mating undercut in the female portion of the opposingconnector 120, 152 to attach the portions using a snap fit. Bayonetfittings may also be used, as friction or interference fittings or othercommon plastic fitments well known to those versed in the art. Further,in addition to or in place of connectors, a connection means can be usedto connect a handle and neck, such as adhesive, melting, ultrasonicwelding or friction welding.

Connectors in a hollow handle have connection features that provideadvantages over connectors made using injection molding, which aretypically solid. First, connection features such as a male insertionfeature may be physically larger in diameter when made hollow than whenmade solid, if the connection features are made from commonthermoplastics. As connection features are made larger in injectionmolding, for example, the time for the part to cool in the moldincreases roughly in proportion to the square of the diameter, and theability to maintain consistent geometry becomes more difficult. Inaddition if the inner cavity extends into the connector the inner cavitysurface may have connector features, such as threading or frictionfittings allowing for complementing connectors, such as in the neck, tobe inserted into the connector. Injection molded parts that are morethan several millimeters thick are also subject to sink marks, which arethe manifestation of solidification-based shrinkage of thermoplasticparts. Sink marks are difficult to control and as such are undesirablein any location where precision geometry is required, for example in asnap-fit or screw-fit connection area, or in any area that will rely oninterference fits to create a water-tight seal. Hollow connectionfeatures are possible in injection molding, and even in injection moldedtoothbrush handles, but in general these must be created or cored fromthe terminal end, and cannot be made hollow and undercut from a singleorifice at the connector end. Injection molded parts hollow at theconnector end will necessarily have their greatest inner diameter at thepoint of connection, and are thus severely limited in geometry.

As illustrated in FIG. 2 the head 160 supports a plurality of cleaningelements, such as bristles or tufts of bristles 162. The bristles ortufts of bristles may comprise nylon, PBT, and TPE. In addition tobristles or tufts of bristles a toothbrush head in the present inventionmay include any suitable cleaning element which can be inserted into theoral cavity. Some suitable cleaning elements include elastomeric massageelements, elastomeric cleaning elements, massage elements, tonguecleaners, soft tissue cleaners, hard surface cleaners, combinationsthereof, and the like. The head may comprise a variety of cleaningelements, and is attached to the handle at the connector end viaconnection features. For example, the head may comprise bristles,abrasive elastomeric elements, elastomeric elements in a particularorientation or arrangement, for example pivoting fins, prophy cups, orthe like. Some suitable examples of elastomeric cleaning elements and/ormassaging elements are described in U.S. Patent Application PublicationNos. 2007/0251040; 2004/0154112; 2006/0272112; and in U.S. Pat. Nos.6,553,604; 6,151,745. The cleaning elements may be tapered, notched,crimped, dimpled, or the like. Some suitable examples of these cleaningelements and/or massaging elements are described in U.S. Pat. Nos.6,151,745; 6,058,541; 5,268,005; 5,313,909; 4,802,255; 6,018,840;5,836,769; 5,722,106; 6,475,553; and U.S. Patent Application PublicationNo. 2006/0080794. Further the cleaning elements can be arranged in anysuitable manner or pattern on the toothbrush head.

In certain embodiments, as shown in FIG. 4 a toothbrush 200 may comprisea handle 210 and neck 212 connected to a head 214; or in certain otherembodiments a toothbrush 230 may comprise a separate handle 232, neck234, and head 236—the separate parts may be connected using one or moreof the methods of connection listed above.

In certain embodiments of the present invention, a toothbrush handle maybe made from multiple layers of material, for example to createdifferent tactile surfaces. Wherein the layers of material may bepresent on or in the toothbrush handle outer surface. Generally, in atwo-layer embodiment, an inner, or substrate, layer is made from a firstmaterial which is the main load-bearing material and is typicallythicker than subsequent outer layers; and an outer layer may be madefrom a softer material which may have a higher coefficient of frictionwith wet or dry skin, or other improved tactile features.

In certain embodiments, as shown in FIGS. 6 and 6A, of a multi-layerpersonal toothbrush handle 300, layers of material may be whollyconcentric, where all or nearly all of the outer surface 332 of an innermaterial layer 320 rests integrally adjacent to the entire or nearlyentire inner surface 331 of an outer material layer 330. In certainembodiments, as shown in FIGS. 7 and 7A, layers of material may varyradially about the perimeter of the outer surface 420 of a toothbrushhandle 400, for example creating a stripe or stripes of a second layermaterial 430 extending along the longitudinal axis of the toothbrushhandle, which may be a different color, hardness, durometer or anycombination thereof from a first layer material 410. In certainembodiments, as shown in FIGS. 8 and 8A, material layers on a handle 500may vary both radially and axially, where one or more layers of materialmay appear as a stripe or stripes 530 extending along the longitudinalaxis (L) of the handle 500. The stripe or stripes 530 overlay an innerlayer of material 520 that contains and forms the inner cavity 510. Incertain embodiments, an outer layer of a second material present on orin the outer surface of a toothbrush handle may be small and occupy lessthan 50%, 40%, 30%, 20%, 20%, or 5% of the circumference of thetoothbrush handle outer surface, as compared to a first layer materialalso present on or in the toothbrush handle outer surface. In anotherembodiment, a tactile layer made from softer or higher-friction materialmay occupy 50% or more of the toothbrush handle outer surfacecircumference.

In certain embodiments of multi-layer toothbrush handles, material layerthickness may vary along the toothbrush handle longitudinal axis, thecircumference, or both. In the case of extrusion blow molding, this canbe accomplished by varying the relative extrusion pressures and/or flowrates of the two or more materials upstream of the extrusion orificeover the course of the extrusion of a single part. As shown in FIGS. 9and 9A the thickness of a first material layer 620 and second materiallayer 630 may vary along the longitudinal axis (L) of a toothbrushhandle 600. In certain embodiments of toothbrush handles 700, as shownin FIGS. 10 and 10A a second material layer 730 may be partially orsubstantially visible through a first material layer 720, whichcompletely or substantially encompasses the second material layer 730.For example the first material layer may be completely or partiallytransparent or translucent. The first material layer 720 may vary inthickness around the circumference of the toothbrush handle 700, suchthat the second material layer 730 is closer to the outer surface 710along portions of the toothbrush handle 700 as compared to otherportions. If the second material layer 730 visibly differs from thefirst material layer 720, for example different color, material, ortexture that difference will be more noticeable in the portions of thetoothbrush handle 700 where the second material layer 730 is closer tothe outer surface 710. For instance, if the second material layer iscolored and the first material layer is translucent the color of thesecond material layer would be more noticeable or more vibrant in theportion of the toothbrush handle where it is closer to the outersurface.

Extrusion blow molded articles with up to seven layers are known tothose familiar in the art, and such layers may serve purposes of vaporbarrier, water barrier, gas barrier, perfume barrier, chemical barrier,recycle content, low-cost material content (i.e. filler), or higher-costmaterial content to include economically color, transparency,translucency, or reaction due to heat or specific or general wavelengthsof light, including infrared, visible and ultraviolet.

Multi-layer extrusion blow molded toothbrush handles that include asofter element, for example a ShoreA hardness between 10 and 80, astheir outermost layer in the region near the connector end may also havethe advantage that the softer material can provide some additionalsealing against an attachable head or neck versus a harder material suchas polypropylene or most other engineering plastics.

To provide tactile grip, in certain embodiments of a multi-layertoothbrush handle made via in-mold labeling, extruded sheets ofhigh-friction or low-durometer flexible material may be first die cutinto a pre-determined shape to form labels or coupons; or such labelsmay be made with three-dimensional textures via injection-molding,thermoforming, or another molding step. The transition between regionsof different tactile grip may be distinct, abrupt, and accurate. Verydetailed designs and shapes are possible for labels. FIGS. 11 and 11Aillustrate an embodiment of a toothbrush handle 800 where a label 830 isintrinsically bonded to an inner layer 820.

Labels may be made thin enough to deform so that labels follow closelythe three-dimensional shape or contours of the toothbrush handle. Labelsmade from a polypropylene-based TPE in the Shore A 30-50 range may beunder 0.25 mm thick when the polypropylene part wall is 1-3 mm thick toensure adequate forming outer surface of the handle. In certainembodiments labels may be pre-textured.

The texture may have a macro structure, micro structure, or both.Macro-structure is defined to comprise texture or features on a lengthscale greater than 0.1 mm such as tactile ribs, bosses, dimples orbumps; and micro-structure is defined to comprise texture or features ona length scale less than 0.05 mm such as grit-blasted textures, mattetextures, witness lines or parting lines. In certain embodiments amulti-layer toothbrush handle may comprise a primary component formingthe majority of the toothbrush handle and a secondary component forminga minority of the toothbrush handle, wherein the second component may beless than 0.4 mm thick as measured normal to either the inner or theouter surface of the layer, and greater than 1 cm² in area. In certainembodiments, the second component is a material with a highercoefficient of friction and lower durometer than the first component,and has a thickness less than 0.2 mm substantially throughout, asmeasured normal to either the inner or the outer surface of the layercomprising the second material, and has a total exposed surface areagreater than 10 cm².

The materials from which a hollow toothbrush handle can be made shouldcomprise one or more of the following characteristics: (1) strength orresistance to bending and axial loading, (2) toughness, as the oppositeof brittleness, (3) Class I medical device requirements, (4) chemicalcompatibility with a variety of toothpastes and active chemistriestherein, (5) chemical compatibility with other components which aretypically attached to toothbrushes such as decals, printed inks, labels,grip elements, head or neck elements and the like, and (6) ability toprocess to a final geometry by extrusion blow molding, injection blowmolding or injection-stretch blow molding. Examples of materials havingone or more of the above characterisitics include polypropylenes; nylons(polyamides); polyethyleneterapthalates; low-density and high-densitypolyethylenes; polyesters; polyvinylchlorides; and engineering plasticssuch as Acrylonitrile Butadiene Styrene [ABS], polyphenylene ether,polyphenylene oxide. Any sub-types of these materials or otherthermoplastics, including blow-molding-grade thermoplastics, with meltflow indices between 0.3 and 3.0 g/10 min are preferred if a blowmolding process is used. Few materials outside of thermoplasts cansatisfy all the requirements, however blow molded metal objects areknown, and some alloys of zirconium can be formed into hollow shapesusing blow molding techniques.

For toothbrushes which are made from multiple materials, in certainembodiments at least one material is from the list named immediatelyabove, and a second material may be composed either from the same listor from any thermoplastic elastomer (TPE) containing materials in theabove list in some fraction, to allow for heat-activated adhesion andimproved grip, deflection, and coefficient of friction with skin.

For toothbrush handles having an inner cavity, such as those made fromextrusion blow molding it is advantageous to cover the fluid blow holeor hole vestige with the toothbrush head or neck to permit sealing andprevent entry of water or contaminants. Further, for toothbrush handlesmade from extrusion blow molding it is desirable to cover not only theblow hole, but also remove or reduce any flash, pinch or fold defectsthat naturally occur during cavity closing, where the extruded parisonouter diameter may be larger than the local mold cavity diameter, priorto blowing. These defects may also occur in needle blowing embodiments,or in calibrated-neck embodiments, or in embodiments which use neither aneedle nor a metal blowing nozzle to form an inner surface of the blownpart.

In certain embodiments a toothbrush handle having an inner cavity mayhave a center of gravity closer to the head than to the geometric centerthan is normally possible with a solid brush of conventional shape,which provides for improved dexterity or ergonomics during brushing, orthe center of gravity can be placed further from the head than ispossible with a solid, homogeneous brush, for example by placement ofpermanently-mounted weights inside the hollow portion of the handle,which provides for example improved tactile response of the forcestransmitted from the teeth to the head to the handle. Such manipulationof center of gravity provides for additional benefits in handling duringbrushing or storage with no compromise to design elements such as shape,material, or color that appear on the outside of the handle. In additiona toothbrush handle having an inner cavity may have a specific gravity,in certain embodiments below about 0.60 g/cm³, or below about 0.20 g/cm³in plastic or about 0.10 g/cm³ in metal, while maintaining a modulus orstrength sufficient to resist bending during even heavy brushing withoutconcern of alignment or particular arrangement of any raw material orload-bearing element (in contrast to materials having a grain, such aswood or carbon fibers), which is difficult to achieve in a toothbrushhandle which is substantially solid and made from common isotropic,homogeneous materials such as plastic or metal.

The toothbrushes of the present invention having an inner cavity canhelp reduce the amount of excessive force being applied to thetoothbrush during brushing, such as when using a typical solid manualtoothbrush or electromechanical toothbrush. It is known to thosefamiliar in the art that sustained, repeated brushing with a standardtufted, manual toothbrush with a force of greater than approximately 5.0N can lead to a loss of gum tissue over time. For instance there existelectromechanical toothbrushes with integrated feedback systems to warnusers when this force is exceeded during use. This suggests that asignificant fraction of toothbrush users apply forces up to 5.0N throughthe toothbrush head. An example toothbrush of uniform, rectangular crosssection made from a solid, homogeneous, isotropic material could bemodeled in grip as shown in FIG. 12. The deflection of the head of thetoothbrush in this grip during bending in use can be approximated fromthe equation used to calculate the flexural modulus of a flat bar ofmaterial in three point bending as shown in FIG. 13, and as disclosed inASTM D 790.

Materials used to form toothbrush handles having an inner cavity (hollowtoothbrushes) should provide a resistance to bending, or stiffness, whena load is applied normal to the longitudinal axis. Toothbrush handlematerials that do not meet this criterion bend severely during normaluse, and result in a negative experience or deliver insufficient forceto adequately clean teeth. To evaluate candidate materials forconstruction of a toothbrush handle in as lightweight an embodiment aspossible, we define here a ratio for the bending strength of the handleto its overall specific gravity as a measured deflection under specificloading case described in FIG. 13.

The chart in FIG. 14 illustrates this ratio applied to a simplerectangular beam-shaped approximation of solid handles made fromisotropic, homogeneous materials; handles made from composite ornon-homogeneous, non-isotropic materials; and hollow-handles made fromotherwise isotropic, homogeneous materials. Results in the chart areobtained from the analytical equation of bending for the apparatus inFIG. 13 or from the predicted bending in a finite-element analysis ofmaterials not solvable in analytical form, such as anisotropicmaterials. It is clear from this chart that solid handles made fromisotropic, homogeneous materials cannot achieve a bendingstrength-to-weight ratio achievable by engineered isotropic, homogeneoushollow handles.

Not all hollow, articles have sufficient bending strength to withstand5N of force applied in bending normal to the major axis at a distancetypical of that applied to a toothbrush between a thumb-fulcrum and thebrush head. Certainly not all blow molded articles can withstand suchforces in any loading situation: many blow molded packages, such aswater bottles, must be filled prior to stacking in pallets as theirwalls are sufficiently thin that they will significantly deform incompression under even the weight of a few empty bottles on top of them.It is possible to make toothbrushes and toothbrush handles in a similarfashion, either through use of generally weak materials or throughmanufacture of extreme thinness of walls, such that they would appearstrong, possibly due to use of opaque materials or other decoration.Toothbrushes made from these handles would not collapse under gravity ormild forces, and could appear robust in packaging or in a non-usedisplay but in fact would be displeasing or impossible to use asintended, or to deliver sufficient brushing force to maintain oralhealth. Generally, toothbrushes or toothbrush handles which deform morethan 40 mm under a 5.0N force applied normal to the head on the surfaceto which bristles are mounted would not be desirable in use. In certainembodiments, the toothbrush handles of the present invention deform lessthan about 40 mm under a 5.0N force applied normal to the head on thesurface to which bristles are mounted. In certain embodiments thetoothbrush handles of the present invention deform less than about 20 mmunder a 5.0N force applied normal to the head on the surface to whichbristles are mounted. A sample bent under loading as defined by ASTM D790 should deflect at the point of loading approximately 25% as much asa sample bent and measured for deflection at the load point shown inFIG. 12, so a sample bent in ASTM D 790 that deflects more than 10 mmunder 5.0N applied load would be considered too weak. In certainembodiments, a sample that deflects more than 5 mm under 5.0N appliedload would be considered too weak.

Isotropic, non-homogeneous materials appear from this chart to becandidates also for lightweight handles, however these materials areintrinsically brittle as a result of stress concentrations due tobubbles which are the result of the foaming process. The chart asdescribed above illustrates only predicted or theoretical deflectionunder load and does not take into account ultimate strength ofmaterials. Toothbrushes made from the foams shown would fracture at thesurface under tension while in bending at loads much less than thoseused during typical brushing.

In general, hollow toothbrush handles with a substantially-uniform wallthickness provide desired resistance to bending with minimal use ofmaterial by placement of the material selectively at the outermostdiameter, or the furthest location from the bending axis, where it canbear the most bending moment, with the least necessary strength. Thisselective placement of material naturally reduces the axial forcesapplied to material elements, caused by bending moments, and results inless strain per material element per unit of applied normal force orbending moment than if the handle is made from solid material or hasmaterial placed primarily in the neutral axis. An I-beam is a commonexample of selective placement of material as far as possible from aneutral axis, however an I-beam resists bending quite differently whenbent around different. A hollow part which is substantially, or evenapproximately round in cross section, such as a hollow toothbrush, willprovide adequate strength in bending about a variety of axes, which isnecessary for a personal care article such as a toothbrush which is handheld and used regularly in many different orientations and must bearloads about nearly any bending axis.

However, not all hollow toothbrush designs would provide sufficientresistance to bending, as defined in the deflection-to-specific-gravityratio above. Rather, it is easier to manufacture an extrusion blowmolded toothbrush with a very thin, flexible wall than it is tomanufacture a toothbrush in such a manner whose wall is thick enough toprovide adequate resistance to bending. For all extrusion blow moldedarticles, there is an upper limit on the thickness of the wall which canbe created without creation of significant folds or flash lines in theexterior surface of the article. This upper limit is governed by thesmallest outer circumference of the portion of the article which is tobe rendered hollow, the starting thickness of the extruded materialprior to blowing, and the ratio of the initial circumference of theblown section to the final circumference of the blown section. As thewall thickness of the starting material increases, a greater fraction ofit may become trapped between mold surfaces intending to mate, thuscreating a flat section around all or a portion of the molded article,commonly known as flash. Hollow toothbrush handles with even smallamounts of flash would be displeasing to use, especially as flashbecomes or feels sharper to the touch the smaller it is.

Elasticity and strength of materials also play a factor in resistance tobending: for example a blow molded toothbrush having sufficientstiffness and made from a relatively strong material, such as PET-G, maybe too weak to be considered useful when molded in the same geometry andwall thickness from LDPE or Polypropylene. Even between LDPE andPolypropylene, a Polypropylene toothbrush may be sufficiently strongerthan an LDPE toothbrush when molded to the same geometry and wallthickness, such as to be noticeably stiffer by a user.

The wall thickness needed to provide sufficient bend strength will varywith material elastic modulus as well as with the distance of thatsection of the wall from the toothbrush axial centerline. To a firstapproximation, a hollow toothbrush with a larger diameter will requireless wall thickness to maintain the same bending strength, however aswall thickness decreases, the potential for catastrophic bending bybuckling or squeezing becomes possible, so there is as well a lowerlimit on wall thickness, even at very large cross sections or diameters.We can define an approximate average wall thickness for the toothbrushas the volume occupied by plastic divided by the average of the innerand outer surface areas of the hollow handle. In certain embodimentsaverage wall thickness may be between is between 0.3 mm and 5.0 mm or1.0 mm and 3.0 mm. In certain embodiments the thickness of thetoothbrush handle wall and the thickness of the individual layers forthose embodiments having two or more layers varies less than about 20%,10% or 5% along the toothbrush handle longitudinal axis.

In certain embodiments of the invention, a polypropylene toothbrushhandle whose length is between 60 mm and 180 mm, and has a weightbetween 7.0 g and 12.0 g with material distributed substantially evenlyabout the wall of the hollow portion, has an overall specific gravityless than 0.5 g/cm³.

In addition to the bending strength, rigidity and convenience inmanufacturing a hollow toothbrush handle is the advantage to using theun-occupied internal volume to house some useful or decorative element.Such elements can include elements common to assembled hollow brushessuch as primarily electronic systems, electromechanical systems,primarily mechanical systems, and decorative elements.

Electronic elements such as batteries, timers, alarms, transducers,accelerometers, lights, speakers, amplifiers, resistors, capacitors,inductors, transistors, circuits, circuit boards, printed electronics,electronic ink and substrates, solder, wires, and similar components canbe pre-assembled into functioning or partially-functioning systems andinstalled into the void area in a hollow toothbrush handle. Such systemscan make particular use of undercuts in the handle, for example byvirtue of placement or position against or near an undercut to providerestriction in motion. Such systems may also take advantage of an innerlayer of a multi-layer system to provide electrical insulation orconductivity or semi-conductivity between elements integrated to thesystem, or to elements outside of the toothbrush cavity. An example ofthis would be an inductive charging system which harvests energy from anexternal electric field by placement and activation of coils of wirepositioned inside of the handle. This is a common method by which powertoothbrushes are re-charged when not in use. Specific embodiments ofthese systems and elements include, but are not limited to: a timer toprovide feedback to a user during brushing of the teeth, a force sensorto discourage excessive use of force during brushing, an indicatorelement informing a user when the expected life of a toothbrush might bereached, lights or sounds to play a song or game during brushing, use ofthe geometric properties of the hollow void to resonate or attenuatecertain sounds generated inside, an electrostatic generator to chargethe system to a high or low potential voltage, creation of an‘electronic pet’ or tamagotchi, which will thrive if good brushinghabits are maintained and suffer or die if they are not, and the like.

Electromechanical systems such as rotating motors, linear motors,permanent-magnet direct current motors, piezoelectric transducers,buttons, toggle switches, temporary switches, magnets, reed switches canalso be used independently, or more likely combined with electricalelements and systems to provide further benefits or feedback to users.Examples include but are not limited to: Use of a motor to create avibrating tactile feedback, use of piezotransducers or inductiveelectrical systems to harvest mechanical energy and convert toelectrical energy during brushing, use of switches to activate anddeactivate electrical or electromechanical systems, use of magnets aselements in inductive systems or to provide detection to an externalelectrical system, use of strain gauges to measure and feedback or useof vibration-inducing motors or offset-weight motors to create apleasing tactile sensation at any point in the brush. For the use ofmechanical switches, it may also provide an advantage to selectivelythin the wall of the toothbrush handle in some areas but not all inorder to create a deformable region which can allow deflection throughthe solid wall of an internally-mounted switch without creating anorifice which must be sealed in an additional step.

Primarily mechanical systems, such as solids, liquids, gasses, colloids,magnets, living or organic elements, phase-change orchemically-transitioning elements, color-change elements,thermochromatic elements, and the like can be installed within a hollowtoothbrush handle, either permanently or with the intention of laterdispensing, for consumption. Examples of consumable filling elementsinclude but are not limited to: Toothpaste, oral rinse, whiteningagents, breath fresheners. Examples of solids include but are notlimited to: Articles shaped and designed to add weight or heft to adevice, such as iron, zinc, or other metals in solid form; silica, orother granular material, in a single color or multiple colors. articlesmade from liquids could include but are not limited to: water, oils,gels, or combinations thereof, including emulsions, mixtures, solutionsand combinations of the above which readily separate, such as oil andwater. Magnets placed in a device may add advantages of storage orconnection/interaction to ferrous materials or articles, for examplecabinetry hardware or refrigerator or household appliance doors. Magnetscan also be arranged internally so that they interact with magnetsoutside the toothbrush to stand the toothbrush on end to prevent thehead from touching any bathroom or other storage area surfaces.Phase-change or color change elements or systems tuned to slightly belowhuman body temperatures may be included into a hollow toothbrush withtransparent outer layers for example to create a non-electric timer,which would permit the toothbrush to change color after sufficient timeheld in the hand.

Separate from installed elements, and an advantage of a hollowtoothbrush handle is the ability to decorate a translucent ortransparent handle on an inner surface which is isolated from contact bythe user via the body of the toothbrush handle. In these embodiments,there would be an advantage in isolating the decorative layer from humancontact, for example to create some delay in the temperature elevationof the isolated layer, i.e. for thermochromatic paint which may changecolor after approximately some set time. Also advantageous would be areduction in the appearance of wear, in contrast to surfaces which arepainted or decaled on the outside surface and subject to mechanical wearand chemical attack.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

Every document cited herein, including any cross referenced or relatedpatent or application, is hereby incorporated herein by reference in itsentirety unless expressly excluded or otherwise limited. The citation ofany document is not an admission that it is prior art with respect toany invention disclosed or claimed herein or that it alone, or in anycombination with any other reference or references, teaches, suggests ordiscloses any such invention. Further, to the extent that any meaning ordefinition of a term in this document conflicts with any meaning ordefinition of the same term in a document incorporated by reference, themeaning or definition assigned to that term in this document shallgovern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. A toothbrush handle comprising: a) a terminalend, connector end, outer surface, inner cavity, and longitudinal axis;b) the inner cavity having a surface defining a cross-sectional area;wherein the inner cavity has at least one of a greater cross-sectionalarea, bordered by two lesser cross-sectional areas along thelongitudinal axis of the toothbrush or a lesser cross sectional areabordered by two greater cross-sectional areas along the longitudinalaxis of the toothbrush; c) the outer surface defining an outer surfacecross-sectional area; d) a wall formed from the outer cavity surface andinner cavity surface; e) the toothbrush handle comprising a singleunitary component; wherein the difference between the outer surfacecross-sectional area and the inner cavity surface cross-sectional areavaries less than 25% over at least 50% of the toothbrush handle lengthalong the longitudinal axis.
 2. The toothbrush handle of claim 1,wherein the square root of the outer surface cross-sectional area variesproportionally to the square root of the inner cavity cross-sectionalarea along the longitudinal axis of the toothbrush.
 3. The toothbrushhandle of claim 2, wherein the square root of the inner cavity surfacecross-sectional area varies proportionally less than 5% to thevariations in the square root of the outer surface cross-sectional areaalong the longitudinal axis of the toothbrush handle.
 4. The toothbrushhandle of claim 1, wherein the in the thickness of the toothbrush handlewall varies in inverse proportion to the square root of the outersurface cross-sectional area.
 5. The toothbrush handle of claim 1,wherein the average wall thickness is from about 0.5 to about 5.0 mm. 6.The toothbrush handle of claim 1, wherein the inner cavity is open tothe outer surface of the toothbrush handle.
 7. The toothbrush handle ofclaim 1, wherein the inner cavity is sealed and is not open to thetoothbrush handle outer surface.
 8. The toothbrush handle of claim 1having a connector.
 9. The toothbrush handle of claim 7, wherein theinner cavity extends into the connector.
 10. The toothbrush handle ofclaim 9, wherein the inner cavity comprises a connection feature. 11.The toothbrush handle of claim 1 having a specific gravity below about0.60 g/cm³ and wherein the toothbrush handle deforms less than about 10mm under a 5.0N force applied as determined by ASTM D
 790. 12. Thetoothbrush handle of claim 1, wherein the outer surface cross-sectionalarea of at least one of the terminal end or connector end is less thanthe largest cross-sectional area of the inner cavity.
 13. The toothbrushhandle of claim 1, wherein outer surface cross-sectional area of atleast one of the terminal end or connector end is less than the smallestcross-sectional area of the inner cavity.
 14. The toothbrush handle ofclaim 1, wherein the toothbrush handle comprises at least one ofpolypropylene, polyethylene terapthalate, polyethylene terapthalateglycol, high-density polyethylene, low-density polyethylene, orpolystyrene.
 15. A toothbrush handle comprising: a) a terminal end,connector end, outer surface, inner cavity, and longitudinal axis; b)the inner cavity having a surface defining a cross-sectional area;wherein the inner cavity has at least one of a greater cross-sectionalarea, bordered by two lesser cross-sectional areas along thelongitudinal axis of the toothbrush or a lesser cross sectional areabordered by two greater cross-sectional areas along the longitudinalaxis of the toothbrush; c) the outer surface defining an outer surfacecross-sectional area; d) a wall formed from the outer cavity surface andinner cavity surface; e) the toothbrush handle comprising a singleunitary component; wherein the toothbrush handle comprises two or morematerial layers.
 16. The toothbrush handle of claim 15, wherein thesquare root of the outer surface cross-sectional area variesproportionally to the square root of the inner cavity cross-sectionalarea along the longitudinal axis of the toothbrush.
 17. The toothbrushhandle of claim 15, having a first material layer and a second materiallayer, wherein the toothbrush handle outer surface comprises the firstmaterial layer and the second material layer.
 18. The toothbrush handleof claim 17, wherein the second material comprises a label.
 19. Thetoothbrush handle of claim 15, having a first material layer and asecond material layer, wherein the second material layer is encompassedwithin the first layer and the second material layer thickness variesless than about 20% along the length of the toothbrush handlelongitudinal axis.
 20. The toothbrush handle of claim 15, having a firstmaterial layer and a second material layer, wherein the second materiallayer is encompassed within the first layer and is visible through thefirst material layer.